Lactotransferrin, also known as Lactoferrin, Talalactoferrin and LTF, is a secreted protein which belongs to the transferrin family. Transferrins are iron binding transport proteins which can bind two Fe3+ ions in association with the binding of an anion, usually bicarbonate. Lactotransferrin has antimicrobial activity which depends on the extracellular cation concentration. Lactoferroxins A, B and C have opioid antagonist activity. Lactoferroxin A shows preference for mu-receptors, while lactoferroxin B and lactoferroxin C have somewhat higher degrees of preference for kappa-receptors than for mu-receptors. Lactoferrin / LTF is a globular glycoprotein that is widely represented in various secretory fluids, such as milk, saliva, tears, and nasal secretions. Lactoferrin / LTF is also present in secondary granules of PMN and is secreted by some acinar cells. Lactoferrin / LTF can be purified from milk or produced recombinantly. Human colostrum has the highest concentration, followed by human milk, then cow milk. Lactoferrin / LTF is one of the components of the immune system of the body; it has antimicrobial activity (bacteriocide, fungicide) and is part of the innate defense, mainly at mucoses. In particular, lactoferrin provides antibacterial activity to human infants. Lactoferrin interacts with DNA and RNA, polysaccharides and heparin, and shows some of its biological functions in complexes with these ligands.